One of the major unresolved questions in biology is the mechanism by which such organic nutrients as sugars are transferred through cellular membranes. Our study is directed towards the identification of the molecules in the membrane, involved in the interaction with sugar during absorption. Two systems are used for the study, the erythrocyte membrane and the intestinal epithelial cell. The mechanism for the sugar absorption in the intestine is localized in the brush border of the intestinal epithelial cell and represents an active process. The erythrocyte membrane can be prepared in inside out and right side out forms and represents a passive transport system. We are using a photoaffinity labeling technique for the identification of the receptor molecules involved. Derivatives of glucose possessing photoreactive groupings have been prepared and shown to interact with the carrier. We are planning to prepare a radioactive molecule for the identification of the components involved. Eventually an unlabeled molecule could be isolated providing us with the means to learn about the nature of its function. This approach could be extended towards the understanding of transport of nonionic organic nutrients in mammalian cells in general.